Many earth-working machines, such as, for example, loaders, tractors, and excavators, include tracked undercarriages to facilitate movement of the machines over ground surfaces. Such undercarriages include drive sprockets that rotate track assemblies about one or more idlers or other guiding components to propel the machines over the ground surfaces. Each track assembly includes a pair of parallel chains, each made up of a series of links, joined to each other by pins and/or bushings (the combination of which is sometimes referred to as a cartridge assembly). Due to extreme wear from abrasion and impacts experienced during use, undercarriage maintenance costs often constitute more than one quarter of the total costs associated with operating the earth-working machines.
FIG. 1 provides an example of a prior art cartridge assembly 10 for coupling links, which is disclosed by U.S. Patent Application Publication No. 2012/0267947 by Johannsen et al. As shown, cartridge assembly 10 includes a pin 12 accommodated within an inner bushing 14, which is, in turn, accommodated within an outer bushing 16. End portions 17a, 17b of inner bushing 14 are surrounded by inserts 19a, 19b, and end portions 21a, 21b of pin 12 are surrounded by collars 23a, 23b. Pin 12 has a lubricant channel 25, which serves as a reservoir for lubricant and delivers lubricant to a gap between pin 12 and inner bushing 14, and to a gap between inner bushing 14 and outer bushing 16. The lubricant is retained by seals 27a, 27b positioned between outer bushing 16 and inserts 19a, 19b, and by seals 29a, 29b positioned between inserts 19a, 19b and collars 23a, 23b. 
Cartridge assembly 10 may provide certain benefits that are particularly important for some applications. However, it may have certain drawbacks. For example, manufacturing pin 12 to include channel 25 may be complicated and costly. As another example, manufacturing links large enough to accommodate inserts 19a, 19b and collars 23a, 23b (as opposed to just pin 12 and inner bushing 14) may require an excessive amount of material. The disclosed embodiments may help solve these problems.